In recent years, there has been a trend in development toward small, highly supercharged engines, wherein supercharging is primarily a method of increasing power, in which the air required for the combustion process in the engine is compressed. The economic significance of said engines for the automotive engineering industry is ever increasing.
For supercharging, use is often made of an exhaust-gas turbocharger, in which a compressor and a turbine are arranged on the same shaft. The hot exhaust-gas flow is supplied to the turbine and expands in the turbine with a release of energy, as a result of which the shaft is set in rotation. The energy supplied by the exhaust-gas flow to the turbine and ultimately to the shaft is used for driving the compressor which is likewise arranged on the shaft. The compressor delivers and compresses the charge air supplied to it, as a result of which supercharging of the cylinders is obtained. A charge-air cooler is advantageously provided in the intake system downstream of the compressor, by means of which charge-air cooler the compressed charge air is cooled before it enters the at least one cylinder. The cooler lowers the temperature and thereby increases the density of the charge air, such that the cooler also contributes to improved charging of the cylinders, that is to say to a greater air mass. Compression by cooling takes place.
The advantage of an exhaust-gas turbocharger in relation to a mechanical charger is that no mechanical connection for transmitting power exists or is required between charger and internal combustion engine. While a mechanical charger extracts the energy required for driving it entirely from the internal combustion engine, and thereby reduces the output power and consequently adversely affects the efficiency, the exhaust-gas turbocharger utilizes the exhaust-gas energy of the hot exhaust gases.
As already mentioned, supercharging serves for increasing power. The air required for the combustion process is compressed, as a result of which a greater air mass can be supplied to each cylinder per working cycle. In this way, the fuel mass and therefore the mean pressure can be increased.
Supercharging is a suitable means for increasing the power of an internal combustion engine while maintaining an unchanged swept volume, or for reducing the swept volume while maintaining the same power. In any case, supercharging leads to an increase in volumetric power output and an improved power-to-weight ratio. If the swept volume is reduced, it is thus possible to shift the load collective toward higher loads, at which the specific fuel consumption is lower. By means of supercharging in combination with suitable transmission configurations, it is also possible to realize so-called downspeeding, with which it is likewise possible to achieve a lower specific fuel consumption.
Supercharging consequently assists in the constant efforts in the development of internal combustion engines to minimize fuel consumption, that is to say to improve the efficiency of the internal combustion engine.
It is a further basic aim to reduce pollutant emissions. Supercharging can likewise be expedient in solving this problem. With targeted configuration of the supercharging, it is possible specifically to obtain advantages with regard to efficiency and with regard to exhaust-gas emissions.
The torque characteristic of a supercharged internal combustion engine can be improved through the use of multiple turbochargers, for example by means of multiple turbines of relatively small turbine cross section arranged in parallel, wherein turbines are activated in succession with increasing exhaust-gas flow rate, or by means of multiple exhaust-gas turbochargers connected in series, of which one exhaust-gas turbocharger serves as a high-pressure stage and one exhaust-gas turbocharger serves as a low-pressure stage.
With regard to the configuration of the exhaust-gas turbocharging, it is basically sought to arrange the turbine or turbines as close as possible to the outlet of the internal combustion engine, that is to say to the outlet openings of the cylinders, in order thereby to be able to make optimum use of the exhaust-gas enthalpy of the hot exhaust gases, which is determined significantly by the exhaust-gas pressure and the exhaust-gas temperature, and to ensure a fast response behavior of the turbocharger. A close-coupled arrangement not only shortens the path of the hot exhaust gases to the turbine but also reduces the volume of the exhaust-gas discharge system upstream of the turbine. The thermal inertia of the exhaust-gas discharge system likewise decreases, specifically owing to a reduction in the mass and length of the part of the exhaust-gas discharge system leading to the turbine.
For the reasons stated above, it is also the case according to the prior art that the exhaust manifold is commonly integrated in the cylinder head. The integration of the exhaust manifold additionally permits dense packaging of the drive unit. Furthermore, the exhaust manifold can benefit from a liquid-type cooling arrangement that may be provided in the cylinder head, such that the manifold does not need to be manufactured from materials that can be subject to high thermal load, which are expensive.
According to the prior art, the turbine that is arranged in the exhaust-gas discharge system may be of different types of construction. The turbine of an exhaust-gas turbocharger is commonly of radial type of construction, that is to say the flow approaching the rotor blades of the impeller runs substantially radially. “Substantially radially” means that the speed component in the radial direction is greater than the axial speed component. The speed vector of the flow intersects the shaft of the exhaust-gas turbocharger at right angles if the approaching flow runs exactly radially. A radial turbine is described for example in EP 1 710 415 A1.
To make it possible for the rotor blades to be approached by flow radially, the inlet region for the supply of the exhaust gas is, according to the prior art, in the form of a spiral or worm housing running in encircling fashion, such that the flow of exhaust gas approaching the turbine impeller runs substantially radially.
For this purpose, it is occasionally necessary for the exhaust gas to be redirected or diverted in order that it can be supplied to the radial turbine. To be able to utilize the exhaust-gas energy in as efficient a manner as possible, however, the exhaust gas should be diverted to the least possible extent. Any change in direction of the exhaust-gas flow, for example owing to a curvature of the exhaust-gas discharge system, results in a pressure loss in the exhaust-gas flow and thus in an enthalpy loss. It is however often also possible for a radial turbine to advantageously be part of the exhaust-gas discharge system, for example as a high-pressure turbine of a multi-stage supercharging arrangement, and the change in direction in the turbine can be utilized to realize a compact design of the supercharging arrangement and of the internal combustion engine.
The turbine of an exhaust-gas turbocharger is occasionally also designed as an axial turbine, that is to say the flow approaching the impeller blades runs substantially axially. “Substantially axially” means that the speed component in the axial direction is greater than the radial speed component. The speed vector in the approaching flow in the region of the impeller runs parallel to the shaft of the exhaust-gas turbocharger if the approaching flow runs exactly axially.
According to the prior art, it is often the case even in axial turbines that the inlet region for the supply of the exhaust gas is in the form of a spiral or worm housing running in encircling fashion, such that, at least in the inlet region, the flow of the exhaust gas runs or is guided obliquely or radially with respect to the shaft. In the case of axial turbines, a diversion of the exhaust gas leads to losses with regard to the available exhaust-gas enthalpy. EP 1 710 415 A1 describes an axial turbine of said type.
In general, turbines are designed to be of so-called mixed-flow type of construction, in which the speed vector of the approaching flow has both a radial speed component and an axial speed component, where a mixed-flow turbine comprises at least one impeller arranged in a turbine housing and mounted on a rotatable turbine shaft. In relation to a purely radial turbine, the mixed-flow turbine is characterized by a lower inertia, which results from the smaller diameter of the impeller.
The mixed-flow turbine may be equipped with a variable turbine geometry, which permits a more precise adaptation to the respective operating point of the internal combustion engine by means of an adjustment of the turbine geometry or of the effective turbine cross section. Here, guide vanes for influencing the flow direction are arranged in the inlet region of the turbine. In contrast to the rotor blades of the rotating impeller, the guide vanes do not rotate with the shaft of the turbine.
If the turbine has a fixed, invariable geometry, the guide vanes are arranged in the inlet region so as to be not only stationary but rather also completely immovable, that is to say rigidly fixed. In contrast, if use is made of a turbine with variable geometry, the guide vanes are arranged so as to be stationary but not so as to be completely immovable, rather so as to be rotatable about their axes, such that the flow approaching the rotor blades can be influenced.
In some examples of a mixed-flow turbine of an internal combustion engine, there may be arranged upstream of the at least one impeller an adjustable guide device which comprises guide vanes that can be rotated by means of an adjustment device. The adjustment device may be a rotatable adjustment ring which is mounted coaxially with respect to the turbine shaft of the mixed-flow turbine, wherein each guide vane is arranged on a guide vane-specific shaft. The guide vanes are kinematically coupled to the adjustment ring via intermediate elements, such that rotation of the ring causes the guide vanes to be adjusted.
WO 2013/116136 A1 describes a guide device and adjustment device of said type in which pivotable levers are used as intermediate elements, each of which is, at one end thereof, connected rotationally conjointly by way of a bore to a guide vane-specific shaft, and at the other, spherical end thereof, mounted movably in a recess of the adjustment ring.
A disadvantage of the described adjustment device is that the levers are directed inward from the adjustment ring, that is to say the adjustment ring is an adjustment ring situated to the outside of the levers. This leads to large diameters of the adjustment ring, which cannot be integrated into the turbine housing but must be arranged adjacent to the housing. The turbine is thus made altogether larger, that is to say less compact; in particular, its length in the direction of the turbine shaft increases considerably.
Furthermore, in WO 2013/116136 A1, the guide vane-specific shafts on which the guide vanes are arranged are of offset design. This leads to a tumbling motion of the guide vanes during the rotation of the guide vane-specific shafts by means of the adjustment ring, that is to say to complex kinematics, which makes it difficult to realize a gapless arrangement of the rotatable guide vanes in the inlet region and makes it impossible to realize the gapless arrangement of the guide vanes in multiple rotational positions.
The inventors have recognized the above issues and provide a supercharged internal combustion engine to at least partly address the issues. In one example, the engine includes an intake system for the supply of charge air; an exhaust-gas discharge system for the discharge of the exhaust gas; and at least one mixed-flow turbine which is arranged in the exhaust-gas discharge system. The mixed-flow turbine includes a turbine housing having an inlet region; at least one impeller arranged in the turbine housing and mounted on a rotatable turbine shaft; an adjustable guide device arranged in the inlet region upstream of the at least one impeller, the adjustable guide device comprising one or more guide vanes, each guide vane arranged on a guide vane-specific shaft; an adjustment device configured to rotate the one or more guide vanes, the adjustment device having a rotatable adjustment ring which is mounted coaxially with respect to the turbine shaft of the mixed-flow turbine, the rotatable adjustment ring having an external toothing; and one or more gearwheels each arranged on a respective guide vane-specific shaft, each gearwheel configured to mesh with the external toothing of the adjustment ring, such that the one or more guide vanes are adjusted by rotation of the adjustment ring.
The rotatable adjustment ring of the internal combustion engine according to the disclosure has an external toothing. As intermediate elements, use is made of gearwheels which are arranged on the guide vane-specific shafts and which mesh with the external toothing of the adjustment ring. In this way, the guide vanes are kinematically coupled to the adjustment ring. A rotation of the ring causes the guide vanes to be adjusted, wherein the toothing ensures a unique kinematic assignment between the rotational position of the adjustment ring and the position of the guide vanes.
The guide vane-specific gearwheels are arranged around the outside of the adjustment ring, that is to say the adjustment ring forms an adjustment ring situated to the inside of the gearwheels. Consequently, the adjustment ring according to the disclosure can be formed with a relatively small diameter. In relation to the adjustment rings known from the prior art, the adjustment ring of relatively small diameter according to the invention can be integrated into the turbine housing, that is to say, in the case of a spiral or worm housing, indented in the direction of the exhaust gas-conducting lines, that is to say arranged adjacent to said lines. The turbine is thus made more compact, less voluminous and shorter in the direction of the turbine shaft. The adjustment ring itself has a lower weight and, owing to its smaller diameter, also a reduced moment of inertia with regard to its rotational movement.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.